Type 1 diabetes (T1D) is an autoimmune disease in which insulin-producing beta cells are destroyed by the immune system. The consequence of beta cell destruction is an inability to regulate blood glucose levels, which ultimately lead to neurological and vascular complications. The long-term goal of this project is to identify factors that can influence the progression of T1D in susceptible individuals, which may improve T1D diagnosis and therapy. We will examine a role for Group A Streptococcal (GAS) infection in modulating the function of antigen-specific B lymphocytes in mouse models of autoimmune diabetes. B lymphocytes recognizing beta cell antigens can promote autoimmune diabetes development. In response to GAS challenge, B lymphocytes produce a large proportion of antibodies recognizing O-linked N-acetyl-D- glucosamine, which can bind self-antigens on beta cells. Interestingly, a strong negative correlation between childhood GAS infection and T1D has been demonstrated in human epidemiological studies, while challenge with a heat-killed GAS preparation leads to diabetes resistance in susceptible mouse and rat models. In fact, the diabetes resistance can be transferred by sera from mice immunized with heat-killed GAS to unimmunized mice, suggesting that factors in the sera, such as antibodies, can protect against T1D development. We hypothesize that infection with GAS can protect as well as promote the development of autoimmune diabetes through mechanisms involving GlcNAc-specific B lymphocytes. To test our hypothesis, we propose the following specific aims: 1) to characterize the response of GlcNAc-specific B cells in autoimmune diabetes, 2) to determine how neonatal GAS challenge affects the development of autoimmune diabetes, and 3) to identify mechanisms by which GlcNAc-specific B cells influence the development of autoimmune diabetes. We will measure diabetes incidence in GAS-immunized and unimmunized wild type (WT) NOD mice, streptozotocin (STZ) treated WT C57BL/6 mice, and STZ-treated C57BL/6 mice transgenic for immunoglobulin'heavy chain (IgH Tg) associated with GlcNAc recognition. The absolute numbers, phenotype, and tissue distribution of GlcNAc-specific B cells, as well as GlcNAc-specific IgM titers, will be measured by flow cytometry, ELISA, ELISPOT, and immunofluorescence microscopy utilizing clonal idiotype markers. This study will attempt to determine how a common infectious organism, Group A Streptococcus, can alter an individual's propensity to develop type I diabetes (T1D). Understanding the mechanisms involved in this link may provide insight on new strategies for earlier diagnosis, treatments, and prevention of T1D.